Adding an ability to set target for mysql user grant.

Change-Id: I793a25750c39f70bb26415e7e6a95100b77773fe
diff --git a/README.rst b/README.rst
index 6221894..db30e37 100644
--- a/README.rst
+++ b/README.rst
@@ -41,6 +41,7 @@
               password: 'password'
               host: 'localhost'
               rights: 'all privileges'
+              database: '*.*'
 
 Galera cluster slave node